Ch. 9 Muscular Sys. I: Histology and Anatomy Flashcards
Functions of Muscular System
Produce movement
Maintain posture
Stabilize joints
Generate heat - shiver
Functional Characteristics of the Muscular System
Excitability / Irritability (action potential)
Contractility (muscle cells contract)
Extensibility (flex , extend)
Elasticity
Classifications and related Structures
See lecture page 71.
Anatomy of Skeletal Muscle
Gross Anatomy of Skeletal Muscle
1. Nerves and Blood Supply
Each muscle is served by a nerve, artery, and one or more veins that profusely through the connective tissue sheaths discussed below.
*Neuromuscular junction NMJ: Site where motor neuron synapses onto individual skeletal muscle fiber (each skeletal muscle fiber is supplied with its own nerve ending that controls its activity unlike cardiac and smooth muscle)
*Highly vascularized: Must have continuous delivery of oxygen and nutrients (via arteries) to meet extremely high energetic demands.
Produce large amounts of metabolic wastes that must be removed (via veins) in order for contraction to remain efficient.
Anatomy of Skeletal Muscle
Gross Anatomy of Skeletal Muscle
2. Muscle fibers surrounded by bundled Connective tissue sheaths
*Support each cell and reinforce muscle as a whole (even prevent bulging muscles from bursting during exceptionally strong contractions)
*From internal to external:
- Endomysium: around a single muscle fiber (areolar loose c.t.)
- Perimysium: around a fascicle (bundle) of fibers (Dense Irr. C.t)
- Epimysium: covers entire skeletal system: dense Irr. C.t.
Fascia, on the outside of the Epimysium that sometimes blends into deep fascia that lies between neighboring muscles or superficial fascia deep to skin. (Dermis)
Clinical: necrotizing fasciitis (flesh eating disease caused by bacterial infection)
- All layers are continuous with one another and with tendons (Epimysium in particular) that join the muscles to bone. This transmits the pulling force to the bone when the muscle fibers contract.
Anatomy of Skeletal Muscle
Gross Anatomy of Skeletal Muscle
3. Skeletal Muscle Attachments
Direct attachment
*Epymysium fuses directly to periosteum on bone or perichondrium on cartilage
Indirect attachment (Epymysium blends into a CT attachment) Tendon (cord) Aponeurosis (sheet)
2 attachment sites:
Origin: proximal, less movement , more stable
Insertion: Distal to origin in limbs, more moveable
Microscopic Anatomy of a Skeletal Muscle Fiber
- Long, cylindrical cell with multiple nuclei
- Huge in size
- Sacrolemma
- Sarcoplasm
- Myofibrils
- Sacromere
- Sarcoplasmic Reticulum and T tubules
Microscopic Anatomy of a Skeletal Muscle Fiber
2. Huge in Size
Diameter ranges from 10-100 micrometers (10x size of an average body cell) and can be as long as 30cm in length.
Microscopic Anatomy of a Skeletal Muscle Fiber
3. Sarcolemma
Contain a lot of myofibrils Plasma membrane of muscle cell Muscular Dystrophy (Duchenne's) Inherited (X-linked recessive) Weakend sarcolemma Muscle fibers atrophy (weakened)
Microscopic Anatomy of a Skeletal Muscle Fiber
4. Sarcoplasm
Similar to cytoplasm of other cells with usual organelles, but also contains:
Glycosomes (stores glycogen): polymer linking of monomer called protein. Store Inside to make ATP uses it rapidly by breaking it down to glucose.
Myoglobin (stores O2): similar to hemoglobin packed inside muscle cell so that they don’t run out of ATP,
Microscopic Anatomy of a Skeletal Muscle Fiber
5. Myofibrils
Highly organized
Myasin Thick red protein band Dark: A band
Actin Thin blue protein band Light: I band
Rod-like structures that run parallel to length of muscle fiber
Extremely densely packed inside Sarcoplasm (accounts for 80% of entire cellular volume)
Contain the contractile units of skeletal muscle cells called sarcomeres, which are made up actin & myosin myofilaments
Aligned to give distinct bands (Striations)
Microscopic Anatomy of a Skeletal Muscle Fiber
6. Sarcomere
Basic contractile unit Functional unit (and smallest contractile unit) of skeletal muscle
Aligned end-to-end down entire length of myofibril (like the centimeters on a meter stick )
Composed of:
Myosin (thick) filaments, ATPase enzymes, Large head groups: link thick& thin filaments during contraction
Actin (thin) filaments, bare zone: lacks actin filaments at rest, Zdiscs
Basic contractile unit
7. Sarcoplasmic Reticulum and T Tubules
Sets of intercellular tubules that participate in regulation of muscle contraction
Sarcoplasmic reticulum (SR): Specialized and elaborate smooth endoplasmic reticulum Stores Ca2+ (2000x higher conc. Than in normal SER) and releases it on demand when muscle fiber is stimulated to contract
T Tubules :(white tubes)
Elongated tubule that conducts nerve-initiated electrical impulses (action potentials) deep into cell interior (Sarcoplasm)
Increases muscle fibers surface area as the lumen of the T tubule is continuous with extracellular space
Ensures every myofibril in the muscle fiber contracts at virtually the same time
- in blue Ca2+ required to be able to bind to actin.
Brief overview of Sliding Filament Theory
See notebook*
Skeletal Muscle Identification
- Muscles contract and pull (never push) on structures they are attached to (a trochanter, tubercle, tuberosity, etc.)
- Action- movements accomplished when it contracts, ex: flexion, extension, etc.
- Interactions: working together to bring about a desired movement.
Whatever one muscle or muscle group can do, another muscle or group of muscles can “undo”
Four functional groups:
* Prime mover (PM)- primarily responsible for desired movement.
- Antagonist- opposes the prime mover, has to relax.
- Synergist- Aids the prime mover by either, helps by adding extra force for same movement. Preventing or reducing undesirable movements.
- Fixator- immobilizes (fixes) a bone or muscle origin so that the PM has a stable base on which to act.
